Electrolysis device

ABSTRACT

The invention relates to an electrolysis device, comprising at least one horizontal electrolytic cell with a housing ( 6 ) and an anode ( 8 ) that has a membrane or a diaphragm ( 18 ), and a cathode ( 9 ) that has a gas diffusion electrode ( 17 ). The device further comprises supply ( 21 ) and discharge ( 23 ) means for gas ( 3 ) which lead to or away from the gas chamber ( 22 ) of the cathode ( 9 ), and supply ( 16; 19 ) and discharge ( 16; 20 ) means for electrolytes ( 1 ) which lead to or away from the first electrolytic chamber ( 4 ) and to or away from the second electrolytic chamber ( 5 ). The anode ( 8 ) and the membrane or the diaphragm ( 18 ) have at least one respective opening for the supply ( 19 ) of electrolytes ( 1 ) to the second electrolytic chamber ( 5 ), and at least one one further opening for the discharge ( 20 ) of electrolytes from the second electrolytic chamber.

[0001] The present invention relates to an electrolysis device that hasat least one horizontal electrolytic cell that has a housing and ananode with a membrane or diaphragm, and a cathode with a gas-diffusionelectrode, as well as means for supplying and discharging gas into orout of the gas chamber of the cathode, and well as means for supplyingand discharging electrolytes into or out of a first electrolyticchamber, and into or out of a second electrolytic chamber, theelectrolytic chambers being separated from one another by the membraneor diaphragm.

[0002] An electrolysis device of this kind is described in EP-A-182 144.In this, the electrolyte is supplied and discharged by way of openingsdisposed on the edge between the electrodes. Because of this, the crosssectional area of the openings is restricted by the dimensions of theelectrodes and the distance between them. Since the spacing between theelectrodes amounts to only a few millimeters, the cross sectional areathat is available for supplying and discharging the electrolyte isrelatively small. For this reason, such electrolysis devices aresuitable only for electrolytic cells that are connected electrolyticallyin parallel, since only small quantities of electrolyte pass throughthese.

[0003] In the case of cells that are electrolytically connected inseries, as is described, for example, in EP-B-0 865 516, the quantity ofelectrolyte that passes through them is greater, in keeping with thenumber of cells, and unacceptable pressure losses can be caused at theopenings because of high electrolyte speeds. This is particularly so ifan electrode is coated with a porous gas-diffusion electrode. Anhydraulic pressure acts on the gas-diffusion electrode as a function ofthe pressure losses at the openings, and this can result in flooding ofthe electrode if the gas pressure on the other side of the electrode isnot great enough. It is true that—generally speaking—gas-diffusionelectrodes are hydrophobic since they contain a considerable quantity ofTeflon that binds the carbon, so that they can in part be loaded withwater columns greater than 500 mm without the water penetrating into thecells. However, practice has shown that this is not the case in anelectrolysis device since, when current is flowing and ions are present,the surface will be wetted even at pressures below 40 mm of watercolumn. In the same way that hydraulic pressure increases as the lengthof pipe line through which there is a flow increases, so the pressureacting on the gas-diffusion electrode increases with the increasingnumber of cells connected electrolytically in series. This results inthe highest pressure being found in the first cell, and the lowestpressure being found in the last cell. In such a case, flooding of thegas-diffusion electrode can only be prevented by maintaining a specificgas pressure in each individual cell.

[0004] In order to permit operation of the cells in a manner that isless costly and thus more economical, and with only one gas pressure, acascade flow has to be generated, i.e., the electrolyte passes inoverflow from the outlet pipe of one cell into the inlet pipe of thenext cell. At the overflow point, which corresponds to anadjustable-height overflow as described in EP-B-0 865 516, the hydraulicpressure falls off so that the pressure is equal in each cell. In thecase of cells with vertical electrodes, this can be achieved by thelengths of the inlet and outlet pipes, which correspond to the hydraulicpressures. In contrast to this, this is not possible in the case ofhorizontal electrodes, such as those described in EP-A-01 82 114 and inEP-B-0 856 516. In the present case, the permissible variation of theacceptable hydraulic pressure is determined by the installed height ofthe cell. As a rule, this amounts to a few centimeters in order to saveboth space and materials. For this reason, one possibility forgenerating only appropriately low hydraulic pressures lies in thestructural enlargement of the inlet and outlet openings. This can beachieved in that the inlet and the outlet openings are not arrangedbetween the electrodes, but rather adjacent to the electrodes, asproposed in EP-A-0 168 600, EP -A-0 330 849 and EP-B-0 865 516. Thecross sectional areas of the openings is then no longer limited by theamount of space between the electrodes, but can be matched to theincreased quantities of electrolyte by the appropriate layout of theframe geometry in the case of electrolytically series connection.However, one disadvantage with such an arrangement of the openings isthe additional requirement for a sealing frame that joins the membraneof the diaphragm to the frame so that it is gas-tight and liquid-tight,in order that the quantities in the individual chambers are preventedfrom mixing. Since it is located between the electrodes, such a framealso means that the distance between the electrodes and will beincreased by the thickness of the frame. This causes the voltage drop inthe electrolytes to increase and increases energy consumption.

[0005] Increasing the spacing can be avoided if the membrane ordiaphragm or—as is proposed in U.S. Pat. No. 4 436 608—even the gasdiffusion electrode is bent round at the sides. However, this entailsthe danger that too great a shear force will act at the corners of theframe, so that the membrane or diaphragm will no longer be tight becauseit has been damaged.

[0006] For this reason, it is the objective of the present invention todescribe an electrolysis device of the kind referred to in theintroduction hereto, in which the above cited problems associated withthe prior art have been resolved, and in particular to describe anelectrolysis device of this kind which is of simple construction and canbe operated economically.

[0007] According to the present invention, this problem has been solved,for example, in that the anode as well as the membrane or the diaphragmeach have at least one opening for supplying electrolytes to the secondelectrolytic chamber, and at least one additional opening fordischarging electrolytes from the second electrolytic chamber.

[0008] In this respect, it is particularly advantageous if the membraneor the diaphragm be clamped so as to be gas and liquid tight in the areaof the electrolyte supply opening and the electrolyte discharge openingin a sealing frame, the thickness of which does not exceed the thicknessof the anode, and on the sealing frames and the seals that lie on theanodes. Such an arrangement entails the advantage that the spacingbetween the electrodes is not affected by this clamping and the shearforces acting on the membrane or the diaphragm are minimized.

[0009] Most of today's electrolysis cells are manufactured from metalbecause, providing appropriate alloys are used, it is possible to ensurelong-term resistance to chemical and mechanical stresses at very hightemperatures. Disadvantages of metal structures are the materials andproduction costs, which are mostly very high and which, as a rule,include costly welding operations. This is particularly the case withcells that use different materials for the anodes and cathodes, forexample chlorine-alkali membrane cells, in which the anode is of atitanium-palladium alloy that is coated with ruthenium oxide, and thecathode is of nickel. Such cells basically comprise an anode and acathode bath with the particular electrodes. In the case of electricalseries connection, the individual baths are welded together, e.g.,through explosive plated, bipolar rails. Ideally, the cells are weldedtogether by way of such rails using a laser, when the welding range orthe temperature zone can be so arranged spatially that any mixing of thedifferent alloys involved, and thus corrosion, can be prevented. It issimpler to manufacture an electrolytic cell if the anode and the cathodeare of identical material, as is the case, for example, with a cell forproducing hydrogen peroxide in alkaline solution using a gas-diffusioncathode. In this case, nickel can be used as the material. In order toobtain a bipolar cell, the electrodes are simply connected to oneanother electrically through connectors or the cell walls themselves. Inthis cell, it is important that when a diaphragm is used at the anodethere be a gas tight partition between the anode and the cathode—as isdescribed in EP-B-0 865 516—so that the gas pressure, which is meant toprevent flooding of the gas-diffusion cathode by the catholyte, does notact on the anolytes. In contrast to a membrane, a diaphragm is liquidpermeable, so that pressure that acts on the anolytes also acts on thecatholytes. Without a partition, the pressure differential would act onthe gas-diffusion cathode and cause flooding. However, installation ofsuch a partition requires a considerable outlay from the standpoint ofmanufacturing technology, since the requirement for gas-tight sealingdoes not permit the use of spot welding, so that the partition must bewelded to the connectors and the cell walls by continuous welds. In mostcases, however, this leads to warping, since the thinnest possiblematerial is selected for reasons of economy, and the welding heat is notdissipated effectively. As is the case with chlorine-alkali membraneelectrolysis, laser welding is recommended because the temperature zonecan be determined very precisely. However, because of costly set up,long preparation times, and the great demands made on its quality, laserwelding is very cost intensive.

[0010] In order to avoid these production and material costs that resultfrom using two metal baths, as in EP-0-A 182 114, for example, a furtherdevelopment of the inventive concept proposes that the housing of theelectrolysis cell be formed from two plastic panels, between which theelectrolysis chambers and the gas chamber are delimited by the use offrame-like seals.

[0011] At the same time, when a plurality of electrolytic cells arearranged one above the other, the middle plastic panel(s) forms or formthe bottom of the upper electrolysis cell and the cover of theelectrolysis cell that is located below.

[0012] The electrolysis supply and discharge channels for the secondelectrolyte chamber can be incorporated in these plastic panels in asimple manner, in particular, by being milled into them. The sameapplies to the electrolyte supply and discharge channels for the firstelectrolyte chamber.

[0013] PP, PVC, and post-chlorinated PVC can be used as the plastic.These plastics are resistant to a number of chemicals, even attemperatures of up to approximately 80° C. The plastic panels can befitted with seals so that the necessary electrolyte and gas chambers areleft between the electrodes and a plastic panel without incurring anymajor expense. Thus, it is possible to dispense with amaterial-intensive version with two baths, and without welding apartition into place.

[0014] In the case of electrolysis operations other than that used forthe electrolysis of peroxide, it is preferred that the plastic panels beof materials that differ from one another since the anolyte and thecatholyte consist of different compounds. Since the anolyte and thecatholyte are routed across the identical plastic panel, these can moreusefully consist of two different plastics.

[0015] In the case of a plurality of electrolysis cells, the electrolytedischarge channels of the upper electrolysis cell can in each instancebe electrically connected to the electrolyte supply channels of theelectrolysis cell located below so as to permit a flow, by way ofexternal connecting lines.

[0016] If plastic panels are used as a housing, it is not possible tosupply current to the electrodes by way of the housing wall since theseare then non-conductive. A conventional electrical connection by way ofconnectors that are located in the electrolyte area should also beavoided, since these would have to be additionally sealed against theplastic panel. It would also be necessary to mill passages into theplastic panel, a procedure that would degrade the rigidity of the panel.

[0017] Accordingly, the present invention proposes that the anode andthe cathode be routed out through the seals that delimit the electrolytechambers and the gas chamber to the outside, and that they be fittedwith their electrical connectors or connections from the anode to thecathode outside the chamber.

[0018] The electrical connectors or connections can also be locatedwithin the plastic panel, and edge recesses or openings can be providedfor this purpose; they can also be arranged externally. The rigidity ofthe plastic panel will not be degraded in this case.

[0019] The materials used for the electrical connectors and connectionscan be selected as desired since these connectors and connections are nolonger exposed to the chemical and thermal stresses generated by theelectrolytes. For this reason, it is possible to use highly conductivecopper, for example, which is not normally used at this location becauseof its poor chemical and thermal resistance. This leads to a favourablereduction of the cost entailed for the number and the dimensions of theelectrical connectors and connections, to which must be added thecorresponding conductor rails to which the electrical connections aremade.

[0020] Particularly easy assembly is ensured if the connectors and/orconnections to the anodes and the cathodes are made by way of clampingelements. Cost-intensive welding is then no longer necessary.

[0021] When gas diffusion electrolysis is used, a major role is alsoplayed by the gas requirement. This must be many times thestoichiometric requirement for the reactions taking place in gasdiffusion electrolysis, so that no losses of efficiency result. In mostcases, the oxygen in a gas diffusion cathode is converted with thehydrogen that is generated at the cathode during the production ofenergy. As a rule, for reasons of economy, air is used in place ofoxygen. Since, as is known, air contains only 21% oxygen,correspondingly larger quantities of it must be introduced into theelectrolysis cell. This requires supply and discharge lines that are ofappropriately large cross-section, which means that the thickness of thecell frame must be increased; this is undesirable. Any reduction of thecross section with a simultaneous increase in the number of lines mustin most instances be precluded for reasons of economy.

[0022] According to another proposal made by the present invention, forthis reason a gas supply channel and a gas removal channel pass throughthe plastic panels that define the electrolysis cell(s) and optionallythe anodes and the cathodes, from above to below, whilst sealing theelectrolyte chambers, and in a flow connection with the particular gaschamber. The cross section of the supply and removal openings can thusbe determined regardless of the thickness of the panel. To this end,there are openings with identical dimensions in the individual plasticpanels and, optionally, in the electrodes, and these are aligned witheach other in order that the gas, for example the air, is distributedwithin the cell stack with the least possible loss of pressure and in amanner that is favorable from the energy standpoint. The openings are solaid out that the required cross-section is available and so thatsufficient material is left over for the flow of current. Because theair flows downward from above, any electrolyte that passes through thegas diffusion electrode by way of minor leaks can be removed. A furtheradvantage of the possibility for converting large quantities of gas isthe increased absorption of the evaporative heat that is generated atthe gas diffusion electrode, so that internal cooling takes place andthis then replaces external cooling and eliminates the costs that wouldbe incurred for a heat exchanger.

[0023] Thus, according to the present invention it is possible toconstruct electrolysis devices for use in gas diffusion electrolysis,and to do so in a simple and economical manner. No costly weldingoperations are needed. The individual parts can be assembled directly atthe intended site of operation, which means that the costs associatedwith intermediate assembly are eliminated and transportation costs canbe reduced. The combination of different materials for the electrodesand plastics means that cells for various electrolysis processes can beassembled in a cost-effective, modular system

[0024] Additional objectives, features, advantages, and possibleapplications for the present invention are set out in the followingdescription of the embodiments, on the basis of the drawings appendedhereto. Either alone or in any combination, all of the features that thedescribed or illustrated herein constitute the object of the presentinvention, regardless of their combination in the individual claims ortheir references.

[0025] The drawing show the following:

[0026]FIG. 1: A diagrammatic representation of an the electrolysisdevice according to the present invention, which is assembled from fourelectrolysis cells;

[0027]FIG. 2: An enlarged view showing a section of a pair of electrodesin the area of an electrolyte supply opening or an electrolyte dischargeopening;

[0028]FIG. 3: a plan view of a sealing frame as is used in FIG. 2.

[0029] The electrolysis device shown in FIG. 1 has four horizontalelectrolysis cells that are stacked one above the other, and a housing 6that is formed from plastic panels 6′, 6″, the uppermost plastic panel6′ forming a cover and the lowest plastic panel 6″ forming a bottom forthe uppermost or lowest electrolysis cell, respectively, whereas themiddle plastic panel 6″ simultaneously forms the bottom of theelectrolysis cell that is located above it and the cover for theelectrolysis cell that is located beneath it.

[0030] Each electrolysis cell has an anode 8 with a membrane or adiaphragm 18, and a cathode 9 with a gas-diffusion electrode 17, a firstelectrolyte chamber 4 being formed by the seals 11, 12, 13 as an anodechamber and a second electrolyte chamber 5 being formed as a cathodechamber, with a gas chamber 22 being formed on the outside of thecathode 9.

[0031] Electrolyte 1 is routed by way of an electrolysis supply channel19′ in the upper most plastic panel 6′ to an opening 19 in the anode 8and to the associated membrane or to the associated diaphragm 18 andthus to the second electrolyte chamber 5. Electrolyte is removed fromthe second electrolytic chamber 3 through an electrolyte removal opening20 into an electrolyte removal channel 20′ which analogously to theelectrolyte supply channel 19′ is milled into the first uppermostplastic panel 6′ and runs from the second electrolyte chamber 5 firstvertically and then horizontally. Corresponding channels and openingsalso provided in the remaining plastic panels, and anodes and membranesor diaphragms. In the same way that the electrolyte 1 is routed througha side supply opening 26 to the outer edge of the uppermost plasticpanel 6′, the electrolyte 1 flows from the electrolyte removal channel20′ laterally to the outside and into a connecting line 20 to the secondplastic panel 6″, which defines the uppermost electrolysis cell as thebottom and then into an electrolyte feed channel which corresponds tothe supply channel 19′ of the uppermost plastic panel 6′, or until theelectrolyte is discharged from the side of the next to last plasticpanel 6″ through an outlet tube 25. Gas, for example, oxygen or air, isrouted downwards into a gas supply channel 21 that passes through all ofthe plastic panel 6′, 6″ of the housing 6 that is sealed off from theelectrolyte chambers 4, 5 so as to be both gas and liquid tight,although there is a flow connection to the corresponding gas chamber 22of the particular electrolysis cell.

[0032] Below, the gas supply channel 21 opens out in the lowest gaschamber. On the opposite side of the stack of electrolysis cells, avertical gas removal channel 23 extends from the first gas chamber 22 asfar as a lower outlet opening in the lowest plastic panel 6′.

[0033] In the middle of the plastic panel 6′, 6″ there is in eachinstance an electrolyte supply or electrolyte discharge opening 16 ofthe first electrolysis chamber 4 (anode chamber) and the associatedelectrolyte supply and electrolyte discharge channels 16′. Thecorresponding channels 16′ can also be milled into the plastic panel 6′,6″ in the same way as the channels 19′, 20′, as well as the gas passageopenings which are aligned with each other and located in the edge areaof the particular plastic panel 6′, 6″ and form the vertical gaschannels 21, 23.

[0034]FIG. 1 also shows that the electrodes 8, 9 are routed out at theside through the seals that define the electrolyte chambers 4, 5 and thegas chamber 22 and are in this way traversed by the vertical gaschannels 21, 23.

[0035] In the outermost edge area, the plastic panels 6′, 6″ areprovided with edge recesses 24 that are aligned with each other. Withinthese, on both sides, both above and below, there are electricalconnectors 8 (above) and the cathode 9 (below) that are connected to thecontact rails 2; in the middle plastic panel 6″ there are electricalconnections 7′ between the cathode 9 and the anode 8 of the electrolysiscells that follow one another.

[0036] The contact rails 2 as well as the connectors 7 and theconnections 7′ can be of a material, such as copper, that possesses goodcurrent-conducting properties. The connectors 7 and the connections 7′can also be secured to the anode 8 and the cathode 9 through clampingelements (not shown herein).

[0037]FIG. 2 shows how sealing is effected in the area of and inelectrolyte supply opening 19 and in an electrolyte discharge opening20. Whereas the gas diffusion electrode coating 17 on the cathode iscontinuous as far as the edge area of the cathode 9, where it is coveredby a sealing element 12; in the area of the openings 19, 20 the membraneor the diaphragm 18 is angled upward so as to lie on a sealing frame 15,which is no thicker than the anode 8. The sealing frame 15 isaccommodated in a large cutout 27 in the anode 8, and internally itdefines the openings 19, 20. Above the angled area of the membrane or ofthe diaphragm 18 there is a sealing element 14 above the anode 8. In thevicinity of the openings 19, 20 the membrane or diaphragm 18 is clampedby the edge that faces the openings 19, 20 between sealing frames 15 andsealing element 14 so as to be gas tight and liquid tight.

[0038]FIG. 3 shows that the sealing frame 50, which is shown in FIG. 2in vertical cross-section on the line II-II is narrow and its shortsides are curved and thus enclose the openings 19, 20. Reference Numbers 1 Electrolyte  2 Contact rails (of copper)  3 Gas, e.g., O₂ or air  4First electrolyte chamber (anode)  5 Second electrolyte chamber(cathode)  6 Housing  6′, 6″ Plastic panels  7′, 7″ Electricalconnectors or connections  8 Anode, cross hatched area covered bymembrane or diaphragm  9 Cathode, cross hatched area covered bygas-diffusion electrode 10 Connecting line 11, 12 Sealing element 13, 14Sealing element 15 Sealing frame 16 Electrolyte supply and dischargeopening of first electrolyte chamber (anode chamber) 16′ Electrolytesupply and discharge channel of first electrolyte chamber (anodechamber) 17 Gas-diffusion electrode 18 Membrane or diaphragm 19Electrolyte supply opening of the second electrolyte chamber (cathodechamber) 19′ Electrolyte supply channel of the second electrolytechamber (cathode chamber) 20 Electrolyte discharge opening of the secondelectrolyte chamber (cathode chamber) 20′ Electrolyte discharge channelof the second electrolyte chamber (cathode chamber) 21 Gas supplychannel 22 Gas chamber 23 Gas discharge channel 24 Edge cutout 25 Outletpipe 26 Supply pipe 27 Cutout

1. Electrolysis device with at least one horizontal electrolysis cell,with a housing (6), the anode of which has a membrane or diaphragm (18)and the cathode of which has a gas-diffusion electrode (17), with meansto supply (21) and discharge (23) gas (3) into or out of the gas chamber(22) of the cathode (9), respectively, as well as means to supply (16,19) and discharge (16, 20) electrolytes (1) into or out of a firstelectrolyte chamber (4), and into or out of a second electrolyte chamber(5), characterized in that the anode (8) as well as the membrane ordiaphragm (18) each have at least one opening for supplying electrolyte(1) to the second electrolyte chamber (6) and at least one additionalopening for discharging (20) electrolytes (1) from the secondelectrolyte chamber (5).
 2. Electrolysis device as defined in claim 1,characterized in that in the area of an electrolyte supply opening (19)and of an electrolyte discharge opening (20), the membrane or diaphragm(18) is clamped by a sealing frame (15), the thickness of which does notexceed the thickness of the anode (8), as well as at the seals (14) thatare close to the frame (15) and the seals, so as to be gas and liquidtight.
 3. Electrolysis device as defined in claim 1 or claim 2,characterized in that the housing (6) of the electrolysis cell is formedfrom two plastic panels (6, 6′, 6″) between which the electrolytechambers (4, 5) are restricted by the use of frame-like seals (11 to 13)4. Electrolysis device as defined in claim 3, characterized in that theplastic panels (6′, 6″) consist of materials that differ from eachother.
 5. Electrolysis device as defined in claim 3 or claim 4,characterized that a plastic panel (6″) consists of two differentmaterials.
 6. Electrolysis device as defined in one of the claims 1 to5, characterized in that when a plurality of electrolyte cells arearranged one above the other, the middle plastic panel (s) (6′, 6″)form(s) the bottom of the upper electrolyte cell and the cover of theelectrolyte cell that is located below.
 7. Electrolysis device asdefined in one of the claims 1 to 6, characterized in that electrolytesupply (19′) and) discharge channels (20′) of the second electrolytechamber (5) are incorporated, in particular milled, into the plasticpanels (6′, 6″).
 8. Electrolysis device as defined in one of the claims1 to 7, characterized in that electrolyte supply and discharge channels(16′) of the first electrolyte chamber (4) are incorporated, inparticular milled, into the plastic panels (6′, 6″).
 9. Electrolysisdevice as defined in one of the claims 1 to 8, characterized in thatwhen a plurality of electrolysis cells are arranged one above the other,electrolyte discharge channels (16′, 20′) of the upper electrolysis cellare in a flow connection with the electrolyte supply channels (16′, 19′)of the electrolysis cell located below, by way of external connectionlines (10).
 10. Electrolysis device as defined in one of the claims 1 to9, characterized in that the anode (8) and the cathode (9) are routed tothe exterior through the frame-like seals (11 to 14) that define theelectrolyte chambers (4, 5) and the gas chamber (2) to the outside, andoutside the chambers (4, 5; 22) are provided with electrical connectors(7) or connections (7′) to each other.
 11. Electrolysis device asdefined in one of the preceding claims, characterized in that theelectrical connectors (7) are connected to upper and lower contact rails(2) that are, for example, of copper.
 12. Electrolysis device as definedin one of the preceding claims, characterized in that the connectors (7)and/or the connections (7′) are accommodated in edge cutouts'(24) of theplastic panels (6′, 6″).
 13. Electrolysis device as defined in one ofthe claims 1 to 12, characterized in that the connectors (7) and/or theconnections (7′) are pressed tightly against the anode (8) and thecathode (9) by way of clamping elements.
 14. Electrolysis device asdefined in one of the preceding claims, characterized in that a gassupply channel (21) and a gas discharge channel (23) pass through theplastic panels (6′, 6″) and optionally the anode (8) and the cathode (9)whilst being sealed off against the electrolyte chambers (4, 5), in aflow connection with the particular gas chamber (22), downwards fromabove.